FDA Approves Mavacamten for Children With Symptomatic Obstructive HCM. The Label Starts at 30 Kilograms.
The Food and Drug Administration approved mavacamten (Camzyos) on Sept. 30 for children with symptomatic obstructive hypertrophic cardiomyopathy who weigh at least 30 kg. The evidence is 44 adolescents and a gradient endpoint, and the boxed warning and REMS apply.
On Sept. 30, the Food and Drug Administration approved mavacamten (Camzyos, Bristol Myers Squibb) for children with symptomatic obstructive hypertrophic cardiomyopathy. The agency described it as the first drug approved to improve functional capacity and symptoms in these patients. The indication now covers adults and pediatric patients who weigh at least 30 kg, about 66 lb. Adults have had access since 2022.
The label sets its threshold by weight, but the trial behind it was built around age. SCOUT-HCM enrolled adolescents 12 to younger than 18, so there are no trial data in younger children who meet the weight cutoff.
What SCOUT-HCM showed
SCOUT-HCM (NCT06253221) was a phase 3, randomized, double-blind, placebo-controlled international trial in 44 patients with New York Heart Association class II or III disease. Bristol Myers Squibb reported that 23 received mavacamten and 21 placebo, once daily for 28 weeks, starting at 2.5 mg for patients weighing 35 to under 45 kg and 5 mg at 45 kg or more. Entry required an LVEF of at least 60 percent and a Valsalva LVOT gradient of at least 30 mm Hg, HCPLive reported.
The primary endpoint was change in Valsalva LVOT gradient at Week 28. As summarized by AJMC from the New England Journal of Medicine report, the least-squares mean change was a 48.5 mm Hg fall with mavacamten and a 0.5 mm Hg fall with placebo, a difference of 48.0 mm Hg (95% CI, 28.3 to 67.7; P<.001).
The approval rests on a 28-week gradient result in 44 adolescents and on adult evidence for the symptom claim. The boxed warning and the REMS apply to children as they do to adults.
Where the evidence is thin
The gradient is a surrogate. The FDA did not cite a pediatric symptom or functional result. It reasoned from adult data, where reduced obstruction came with better function and symptoms, that mavacamten is "expected to improve" both in children who weigh at least 30 kg.
Secondary echocardiographic results, including resting and postexercise gradients, favored mavacamten, but HCPLive reported that their confidence intervals were not adjusted for multiplicity. Twenty-three treated patients over 28 weeks also say little about long-term exposure or growth. The trial's lowest starting-dose band began at 35 kg, while the label begins at 30 kg, so check the prescribing information for dosing in the lightest patients.
Safety and the label
Camzyos carries a boxed warning for heart failure. In SCOUT-HCM, no patient had an LVEF below 50 percent and no adverse event led to discontinuation, according to the company. Serious adverse events occurred in two patients in each arm. In the mavacamten group, one patient had two episodes of syncope and another received an inappropriate implantable cardioverter-defibrillator shock, Contemporary Pediatrics reported. The FDA lists dizziness and fainting as the adverse reactions above 5 percent that occurred more often than with placebo.
With 23 treated adolescents, zero LVEF events does not rule out the systolic dysfunction seen in adults. Joseph Rossano, MD, chief of cardiology at Children's Hospital of Philadelphia and the trial's principal investigator, called the approval "a landmark moment for pediatric cardiology" in the company's announcement.
What practices should do now
Camzyos is available only through a REMS. Prescribers must review the program materials, pass a knowledge assessment and submit an enrollment form. Each patient is enrolled with a form documenting a baseline echocardiogram, a screen of prescription and nonprescription drugs and supplements for CYP2C19 and CYP3A4 interactions, and authorization for treatment. Follow-up echocardiograms are required at 4, 8 and 12 weeks and then every 3 to 6 months, and only certified pharmacies dispense the drug.
Referring practices can help in three ways. Confirm the patient's current weight against the 30 kg cutoff. Send pediatric cardiology a complete medication and supplement list, since the REMS requires the interaction screen and new inhibitors trigger repeat echoes. And ask whether the receiving center is certified and can run serial echocardiograms close to home, the same planning that applies to other pediatric cardiac therapies.
Reported, fact-checked and edited by The Script Pad's editorial staff.
This article is for professional education and does not replace clinical judgment. Treatment decisions should be based on the individual patient and current guidelines.
